Many devices make use of an encoder strip. A swath type printing device, for example, has a print mechanism that travels along a scan-axis across a print medium in order to print a row of markings on the medium. To print fully on a sheet of the medium, the print mechanism commonly travels a multiple number of times along the scan-axis, each time printing a separate set of rows.
The print mechanism conventionally determines its position along the scan-axis by referencing position markings on a printer encoder strip. A sensing device senses encoder strip markings as the print mechanism travels along the printer scan-axis. The sensing device is usually part of or attached to the print mechanism, and therefore travels along the scan-axis with the print mechanism. The encoder strip is usually stationary. Circuitry or logic within the printer interfaces with the sensing device to determine actual positions of the print mechanism relative to the stationary encoder strip.
A printing device may either be pre-programmed with the extent of its feasible travel along the scan-axis, or may alternatively initialize the extent of its feasible travel along the scan-axis in a calibration procedure. During such a calibration procedure, the printer scans the encoder strip to determine the number of encoder strip markings, and from this information determines the extent of the print mechanism travel along the scan-axis.
Over time, the number of encoder strip markings that can be detected may change as a result of degraded or absent markings on the encoder strip. As a result of this changed number of sensed markings, the position of the print mechanism along the scan-axis cannot be accurately determined, the print mechanism cannot therefore be accurately positioned, and the printing quality of the printing device can be degraded.